Starting and overload control



Sept. '14-, 1965 H- F. GLARK STARTING AND OVERLOAD CONTROL Filed (361.. 50, 1962 INVENTOR.

m BY a 'b His Afforne y MM 5 3 9 E 2:222:25: 8 w F a v J B 4 W 8 7 8 AW 8 n w i i M ,0 Jr A M m a o G u m o o o lc I m 0/ m \M M F M 6 u a mw a 1 M PM 2 M 5 9 w \m W w t m o T0 .6 2 4 Q m 6 8 F 3 3 United States Patent 1 3,206,574 STARTING AND OVERLOAD CONTROL Harry F. Clark, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Oct. 30, 1962, Ser. No. 234,093 4 Claims. (Cl. 200-88) This invention relates to electrical apparatus and more particularly to controls for sealed, internally springmounted, electric motor-compressor units and other electric motor applications requiring better overload protection.

Noise and vibrations are minimized by sealed, internally spring-mounted, electric motor-compressor units. However, the danger of excessive motor temperatures is increased in such units :since a less effective heat transfer between the motor and the sealed casing for the dissipation of heat is inherent in this construction. Consequently, to properly protect the motor under overload conditions, it is necessary to provide an overload protector which will trip quicker and reset more slowly to decrease the heating periods and to increase the cooling periods of the motor during overloads so as to reduce the average temperature and the average ON time. It is therefore an object of this invention to provide a control for an electric motor which will trip quicker under stalling and starting conditions and yet permit the motor to carry the full rated load under normal conditions.

It is another object of this invention to provide a control for electric motors which, upon an overload, energize a supplementary heater in heat transfer relation with the thermal overload protector to cause the overload prot ctor to trip quicker and for supplying heat to the thermal overload protector during and after tripping to delay the resetting thereof so as to provide a longer cooling period before subsequent resetting.

These and other objects are attained in the form shown in the drawings in which the thermal overload protector is provided with a supplemental heater which is located adjacent to the operating bimetal of the protector. The magnetic starting relay is provided with a bimetal arrangement in which the current to both the main and starting windings flows through a bimetal which is arranged to open the starting contacts in the event that the closed period of the starting contacts is too long due to low voltage or other possible causes. This bimetal is also arranged to effect the opening of a set of contacts which are arranged in shunt with the supplemental heater so that, upon an excessive current flow through this bimetal, r

the shunting contacts will be opened to cause the current to flow through the supplemental heater to cause the quicker tripping of the overload protector and, also, the heat stored in the supplemental heater will prolong the resetting time of the thermal overload protector. The shunting contacts are also opened when the armature of the electromagnetic starting control is energized so that the supplemental heater is also energized during the starting period of the motor so as to provide a quicker trip and a longer reset in the event that the motor stalls or is overloaded during the starting period. These two arrangements provide adequate protection for an internally spring-mounted, sealed, motor-compressor unit by the provision of the quicker tripping and longer resetting under overload and starting conditions. During normal operation, the shunting contacts remain closed thereby deenergizing the supplemental heater and allowing a full load upon the motor and prorating of the overload protector.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a plan view of an electric motor starting control and overload protector embodying one form of my invention shown in the deenergized position;

FIGURE 2 is a plan view of the same control showing the control during the starting period with the armature attracted by the electromagnet and the supplemental heater energized;

FIGURE 3 is a plan view of the control similar to FIGURE 1 but showing the control immediately after the tripping of the overload protector due to an overload during the running period;

FIGURE 4 is a fragmentary sectional view showing the bimetal overload actuator of the shunt contacts; and

FIGURE 5 is a wiring diagram of the control connected to a split phase electric motor.

Referring now more particularly to the wiring diagram, FIGURE 5, there is shown a supply conductor 20 connected to the junction 22 connecting to one terminal of the main winding 24 and one terminal of the phase winding 26 of the electric motor 28. The second terminal of the main winding 24 connects to the main winding terminal 30 of the starting and overload control 32. The second terminal of the phase winding 26 connects to the phase or starting terminal 34 of the control 32. The second supply conductor 36 is connected through some type of normal control switch 38, such as a thermostat switch, to the line terminal 40 of the starting and overload control 32. As shown in FIGURES 1 to 3, the terminal 40 rivets the L-shaped contact 42 to the rectangular base 44 of electrical insulating material. The cantilever bimetal 46 carries a contact which is normally held in engagement with the L-shaped contact 42 by a C-shaped toggle spring 48. The C-shaped toggle spring has a second connection with an inverted L-shaped canti lever bimetal compensating strip 50 having its lower end anchored to an irregular frame 52 of heavy metal which is riveted to the base 44.

The cantilever bimetal 46 has an L-shaped extension 54 which is fastened to the frame 52 at the point 60. It is adjusted to vary its tripping point by the adjusting screw 56. The adjusting screw 56 is frictionally held by the spring clip 58 to prevent undesired or accidental adjustment. Beyond the fastening point 60, the bimetal extension 54 continues as a narrow bimetal leg 62 substantially parallel to the bimetal leg 46. At the extreme end of the bimetal leg 62, there is fastened a wide compensating bimetal leg 64 extending in the opposite direction pro- Viding ambient temperature compensation for the leg 62. Fastened to the opposite end of the compensating leg 64 is a spring contact member 66 of thin spring metal provided with a U-shaped portion carrying a contact which is adapted to be inherently sprung against the L-shaped contact 68 riveted to the base 44 by the starting or phase winding terminal 34. This spring contact arm 66 has an extension 70 which is adapted to exert a spring thrust against the lead weighted end 72 of the armature 74 mounted as a cantilever upon a leaf spring 76 fastened to an extension 78 of the frame 79 which also serves as a core for the electromagnet 80. The armature 74 is also provided with a felt cushion 82 to prevent chattering and noise because of the AC. power source supplied to the electromagnct 80.

When the electromagnet 80 attracts the armature 74 as shown in FIGURE 2, the armature 74 moves out of engagement with the spring contact member 66 so that the contact member 66 is not aifected by any chattering of the armature 74 and the contact with the starting contact 68 is made through the spring bias of the spring contact member 66. The extension 70 of the spring contact arm 66 serves to provide spring force to assist the magnetic force provided by the electromagnet 80 in moving the armature 74 out of the unattracted position shown in FIGURES 1 and 3 to the attracted position shown in FIG- URE 2. This assists in making the control operate upon relatively low line voltages under which the magnetic attraction is so weak as to require the assistance of the contact arm 66 and its extension 70 to complete its movement. The contact 68 connects through the terminal 34 to energize the phase winding 26 during the starting period. Both the starting or phase winding current and the main winding current normally flow through the bimetal legs 62 and 64 except during the starting period of the motor or after an overload sufficient to affect the bimetal leg 62. As shown in FIGURE 2, the starting or phase winding current flows from the leg 64 through the long spring contact arm 66 to the starting or phase contact 68 and the terminal 34 to the phase Winding 26.

Also fastened to the bottom of the bimetal compensating leg 64 is a short spring contact arm 84 carrying at its upper end a contact 85 which is adapted to cooperate with a contact 86 provided on the armature 74. The armature 74 is connected through its biased spring mounting strip to the frame 7 8 constituting the core of the magnet 80. The spring mounting strip 76 lightly biases the armature 74 to its unattracted position as shown in FIGURES 1 and 3. It also carries the current from the contact 86 and the armature 74 to the frame 78 to which is attached by welding the terminal 88 of the magnet 80. The opposite terminal 90 of the electromagnet 89 is connected to the main winding terminal 30. This main winding terminal 30, of course, connects to one end of the main winding 24.

According to my invention, the frame 52 is provided with an irregular arm terminating in an upwardly extending stop projection 94 on the opposite side of the cantilever bimetal arm 46 from the L-shaped contact 42. This stop projection 94 serves to limit the opening movement of the bimetal 46 and serves as a resetting control in connection with the C-shaped toggle spring 48 and the compensating bimetal 50 to determine the resetting time of the overload bimetal cantilever arm 46. However, the mechanics of the toggle arrangement is such that there is some limit to this open setting in order to provide a reliable resetting point. Consequently, in addition to this stop projection 94, I provide a supplementary heater in the form of a U- shaped strip heater 96 of Nichrome or similar electrical heater material connected at one end to the projection 94 and connected through the conductor 98 to an unattracted position, limit stop 121 for the contact arm 66 and the armature 74 as shown in FIGURES 1 and 3. This L- shaped stop 121 is welded to the adjacent portion of the armature frame 78 through which the current passing through the heater 96 flows until it meets the connection at the weld point 88 with the terminal of the electromagnet 80.

In operation, the starting control and overload protector normally assume the positions shown in FIGURE 1 during the idle period of the motor which is normally occasioned by the opening of the control switch 38. The armature 74 is unattracted and is biased by the spring hinge 76 to engage the spring extension 76 to move the contact arm 66 away from the cooperating contact 68 to deenergize the starting or phase winding 26. The contact 86 is in engagement with the contact 85 at the upper end of the short spring contact arm 84 to close a shunt circuit for shunting and deenergizing the supplementary heater 96. When the switch 38 closes, current flows from the supply conductor 36 through the terminal 40, the overload cantilever bimetal arm 46 to the irregular'frame 52, thence through the narrow bimetal 62, the compensating bimetal 64, the spring contact arm 84, throughthe contact 86 and through the armature74, the spring member 76 and the electromagnet frame 78 to the terminal 86 of the electromagnet 80 through which the current flows. After flowing through electromagnet 80, the current flows 4 through the terminal conductor 99 to the main winding terminal 39 from which the current flows through the main winding 24 to the junction 22 connecting with the second supply conductor 26.

This control is designed to operate effectively on normal voltages as well as extremely low voltages. This low voltage operation is provided through the arrangement by which the spring contact arm 66 is biased to close position, thereby aiding the weakly energized electromagnet 89 in magnetically attracting the armature 74 against the bias of its spring mounting 76. When the spring contact arm 66 engages the contact 7 8, the projecting end 70 continues to assist the armature 74 in its movement for a short distance until the armature 74 is close enough to the electromagnet 89 to be sufficiently attracted thereby and pulled to the attracted position shown in FIGURE 2 under low voltage conditions. The attraction provided by the electromagnet 8t) pulls the armature 74 away from the extension 76 of the contact arm 66 so that the full bias of the contact arm 66 against the contact 68 maintains full contact pressure without any interruption during the entire starting period of the motor. This prevents damage to the starting contacts.

The attraction of the armature 74 also pulls the contact 86 away from the contact at the upper end of the contact arm 84. This forces the main winding current to flow through an alternate shunt path through the frame 52, the arm 92, the stop 94, the electric heater 96 supplementing the self-heating of bimetal arm 46, through the conductor 98, the L-shaped stop member 121 and the major portion of the frame 79 of the electromagnet 80 to the terminal 88. The supplementary heater 96 therefore, during this period, adds to the self-heating provided by the flow of the line current through the cantilever bimetal arm 46 to provide quicker tripping during the starting period of the electric motor 28. During this period, heat is also stored in the heater 96. Should there be a stall or an unusually heavy starting load, sufficient in amount to overload the motor 28 and its windings 24 and 26, as a result of the heat provided by the heavier current flow through it and the heat added by the heater 96, the cantilever bimetal 96 will snap away from the line contact 42 to the open circuit position shown in FIGURE 3 against the stop 94, thereby deenergizing all circuits. The heater 96, however, will have stored up a certain amount of heat at the time of tripping upon such an overload which will continue to provide heat at a diminishing rate to the bimetal 46 for a period of time to prolong the enforced idle period after the separation of the overload protector contacts 46, 42 to allow further cooling of the electric motor 28 before an attempt is made to restart. This prevents the motor 28 from becoming too hot due to a premature subsequent attempt to restart following an overload.

If there is no overload during the starting period, the reduced current flow through the main winding 24 and the electromagnet coil 80 as a result of the increase of the speed of the motor beyond the balancing speed will sulficiently reduce the magnetic attraction upon the armature 74 to allow it to return to the position shown in FIGURE 1, thereby separating the starting contacts 68, 66 to deenergize the phase winding 26. In addition, the contacts 86, 84 will reclose to shunt the supplementary heater 96 and thereby substantially deenergize the heater 96 so as to discontinue its heating effect upon the cantilever bimetal arm 46. This will adjust the tripping point of the cantilever bimetal arm 46 so that full load and full current flow will be permitted through the overload protector contacts 42, 46 without causing tripping.

However, should there be an overload during this period, the self-heating provided by the increased flow of current through the bimetal leg 62 beyond the full load current will cause it to bow to the right to cause the contact arm 84 to be moved away from the contact 86 to p n t e s nt for the heater 96 and thereby to rcenergize the heater 96 to assist the cantilever arm 46 to open quickly to protect the motor 28 from the overload. The self-heating of the bimetal leg 62 during a prolonged starting period also assists in moving the spring contact member 66 to the open circuit position if this contact member remains in closed position for an excessively long period of time such as may occur under low voltage conditions. The leg 62, therefore, assists in better protecting both the phase winding 26 and the main winding 24 during both the starting and the running periods. It makes the supplementary heater 96 effective even if there should be a defective capacitor or a broken wire or a failure to close the phase winding circuit contacts 42, 46 upon an attempt to start. During the starting period, the current in the main winding falls to reduce the amount of heating of the leg 62 to minimize nuisance tripping due to heat provided by the supplementary heater 96.

While the embodiment of the present invention, as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A control for an electric motor, said control including a self-resetting thermal overload protector for deenergizing said motor upon an overload, an electromagnet coil connected in series with said protector, an armature having attracted and unattracted positions associated with said coil, a low resistance electric heater thermally associated with said thermal overload protector connected in series circuit with said protector and said coil, a spring biased contact means located in the path of movement of and operated by said armature, said contact means ineluding a first set of contacts operated to open position by said armature in its unattracted position and biased to closed position in the attracted position of said armature, said contact means also including a second set of contacts operated to closed position by said armature in its unattracted position and operated to open position by said armature in its attracted position, and means connecting said second set of contacts in shunt circuit with said electric heater.

2. A control for an electric motor, said control including a self-resetting thermal overload protector for deenergizing said motor upon an overload, an electromagnet coil connected in series With said protector, an armature having attracted and unattracted positions associated with said coil, a low resistance electric heater thermally associated with said thermal overload protector connected in series circuit with said protector and said coil, a spring contact arm having a self-heated bimetal section electrically connected to said overload protector, said arm being located in the path of movement of and operated by said armature, said arm having first and second contacts, a normally stationary contact adapted to be engaged by said first contact, said arm having an inherent bias biasing said first contact into engagement with said stationary contact in response to movement of said armature into the attracted position and operated to separate said first contact from said stationary contact by said armature in its unattracted position, a cooperating contact mounted upon said armature for engagement with said second contact, said cooperating contact being electrically connected to said coil.

3. A control for an electric motor, said control including a self-resetting thermal overload protector for deenergizing said motor upon an overload, a normally stationary contact, a spring contact arm normally biased into engagement with said stationary contact, an electromagnet coil and an armature associated with said coil located on the opposite side of said stationary contact from said contact arm, said armature being biased when unattracted into engagement with said contact arm to move said contact arm out of engagement with said stationary contact, said coil being associated in magnetic relationship when energized with said armature to attract said armature away from said stationary contact, said armature having a face facing said contact arm provided with a contact engaging said contact arm in its unattracted position, and an electric heater thermally associated with said overload protector connected in shunt circuit with said contact upon said armature and said contact arm and connected in series with said overload protector and said coil.

4. A control for an electric motor, said control including a base of insulating material, a self resetting thermal overload protector comprising a metal protector frame mounted upon said base and a snap acting bi-metal means mounted on said frame, a first normally stationary contact mounted on said base for cooperation with said bimetal means, said frame being provided with an extension extending on the opposite side of said bi-metal means from said stationary contact to form a stop for said bimetal means, a relay comprising a relay frame of magnetically permeable material mounted on said base and having an electromagnet coil wound thereon having one end electrically connected to said frame, an armature associated with and electrically connected to said frame and coil, an electric heater extending alongside in heating relationship with said bi-metal means having one end connected to said extension and the opposite end connected to said relay frame, a contact member electrically connected to said protector frame provided with two contacts, said armature being provided with a contact cooperating with one of said contacts on said contact member for shunting said electric heater, and a second normally stationary contact mounted on said base cooperating with another of said contacts on said contact member.

References Cited by the Examiner UNITED STATES PATENTS 2,364,603 12/44 Coxon et al. ZOO-88 2,568,476 9/51 Weirich 20088 2,690,485 9/54 Swan 20088 2,731,587 1/56 Brightman 318221 2,740,923 4/56 Loeber 20088 2,786,171 3/57 Clark 318221 3,082,304 3/63 Brock et al 20088 FOREIGN PATENTS 455,542 3/49 Canada.

BERNARD A. GILHEANY, Primary Examiner.

ORIS L. RADER, ROBERT K. SCHAEFER, Examiners. 

1. A CONTROL FOR AN ELECTRIC MOTOR, SAID CONTROL INCLUDING A SELF-RESETTIONG THERMAL OVERLOAD PROTECTOR FOR DEENERGIZING SAID MOTOR UPON AN OVERLOAD, AN ELECTROMAGNET COIL CONNECTED IN SERIES WITH SAID PROTECTOR, AN ARMATURE HAVING ATTRACTED AND UNATTRACTED POSITIONS ASSOCIATED WITH SAID COIL, A LOW RESISTANCE ELECTRIC HEATER THERMALLY ASSOCIATED WITH SAID THERMAL OVERLOAD PROTECTOR CONNECTED TO SERIES CIRCUIT WITH SAID PROTECTOR AND SAID COIL, A SPRING BIASED CONTACT MEANS LOCATED IN THE PATH OF MOVEMENT OF AND OPERATED BY SAID ARMATURE, SAID CONTACT MEANS INCLUDING A FIRST SET OF CONTACTS OPERATED TO OPEN POSITION BY SAID ARMATURE IN ITS UNATTRACTED POSITION AND BIASED TO CLOSED POSITION IN THE ATTRACTED POSITION OF SAID ARMATURE, SAID CONTACT MEANS ALSO INCLUDING A SECOND SET OF CONTACTS OPERATED TO CLOSED POSITION BY SAID ARMATURE IN ITS UNATTRACTED POSITON AND OPERATED TO OPEN POSITION BY SAID ARMATURE IN ITS ATTRACTED POSITION, AND MEANS CONNECTING SAIDSECOND SET OF CONTACTS IN SHUNT CIRCUIT WITH SAID ELECTRIC HEATER. 